Minimize Allocations

General Usage Performance
1

Hi! How do I minimize allocations here? I thought that since all variables involved here are scalars, there should be minimal allocations?

function ϕfield!(
    ϕn::Array{FT}, ϕ::Array{FT}, u::Array{FT}, v::Array{FT},
    G::Grid{FT}, D::Domain{FT}, S::Simulation{FT}, Q::Array{FT}
) where FT <: Real

    for jj = 1 : G.ny, ii = 1 : G.nx

		@timeit "Line 1" vy = (v[ii,jj+1] - v[ii,jj]) / G.δy

        if ii != 1
			@timeit "Line 2" ux = (u[ii,jj] - u[ii-1,jj]) / G.δx
		else
			@timeit "Line 3" ux = (u[1,jj] - u[G.nx,jj]) / G.δx
        end

        @timeit "Line 4" ϕn[ii,jj] = ϕ[ii,jj] - S.δt * (D.α * ϕ[ii,jj] + D.g * D.H * (ux+vy) + Q[ii,jj])

    end

    return

end

Returns

 ──────────────────────────────────────────────────────────────────
                           Time                   Allocations      
                   ──────────────────────   ───────────────────────
 Tot / % measured:      58.1s / 1.43%           1.48GiB / 27.2%    

 Section   ncalls     time   %tot     avg     alloc   %tot      avg
 ──────────────────────────────────────────────────────────────────
 Line 4     1.23M    350ms  42.0%   285ns    225MiB  54.5%     192B
 Line 1     1.23M    252ms  30.3%   205ns   93.8MiB  22.7%    80.0B
 Line 2     1.22M    229ms  27.6%   188ns   93.3MiB  22.6%    80.0B
 Line 3     6.40k   1.17ms  0.14%   183ns    500KiB  0.12%    80.0B
 ──────────────────────────────────────────────────────────────────
2

Indeed, there should be no allocations there. Can you provide a minimal working example? It might be that some of your types are not declared in a type-stable form.

3

I figured out why!! G.nx and G.ny were called as Integer types instead of Int. Thanks for the hint!

1 Like
4 
@code_warntype

is always your friend